Using rodents as a model system, considerable information has been obtained concerning the cellular and molecular basis of mammalian sperm-egg interaction. The long-term objective of this laboratory is to apply this knowledge to contraception and problems of infertility in humans. The specific aim of the proposed study is to obtain a mouse monoclonal antibody, directed against the human sperm, which has the property of binding to a sperm surface protein and inducing the sperm's acrosome reaction, a membrane fusion event in which the plasma membrane overlying the sperm head is lost. Hybridoma cell lines, derived from virgin female mice which had been immunized with acrosome-intact human sperm, will be screened for secretion of antibodies which induce the human sperm acrosome reaction. Since capacity to undergo the acrosome reaction is one measure of sperm fertility. such a monoclonal antibody could potentially be used in clinical assays for detection and treatment of defects in human sperm. This monoclonal antibody could also be used as an immunocontraceptive, if sperm within the female reproductive tract which undergo a premature acrosome reaction are rendered infertile.